Hi. On Thu, Jul 11, 2019 at 03:00:57PM +0000, Andy Smith wrote: > On Thu, Jul 11, 2019 at 05:12:03PM +0300, Reco wrote: > > On Thu, Jul 11, 2019 at 12:03:53PM +0000, Andy Smith wrote: > > > I think the wiki article at > > > https://wiki.debian.org/BoottimeEntropyStarvation really shows that > > > currently there is no such consensus available, as every solution > > > listed (except buying extra entropy hardware) > > > > That one is bad too. > > Hardware random generator is not used by kernel directly, it requires > > userspace program (such as hwrngd). > > So, even if you put it into initrd alongside with the needed kernel > > modules, there's still a noticeable delay between 'kernel rng is needed' > > and 'sufficient entropy is available'. > > With no modifications and RDRAND instruction disabled,
RDRAND is an exception to this as kernel does use it directly if allowed. Devices that I wrote about are exposed to userspace via /dev/hwrng character device. For instance, this Exynos ARM SOC comes with HWRNG, but: [ 0.000000] random: get_random_bytes called from start_kernel+0x9c/0x528 with crng_init=0 [ 0.772543] random: fast init done [ 9.006398] random: lvm: uninitialized urandom read (4 bytes read) [ 10.206032] random: lvm: uninitialized urandom read (4 bytes read) [ 10.363308] random: lvm: uninitialized urandom read (4 bytes read) [ 10.439771] random: lvm: uninitialized urandom read (2 bytes read) [ 12.322888] random: lvmconfig: uninitialized urandom read (4 bytes read) [ 12.861180] random: systemd: uninitialized urandom read (16 bytes read) [ 12.878890] random: systemd: uninitialized urandom read (16 bytes read) [ 14.126267] random: crng init done [ 14.714783] exynos-trng 10830600.rng: Exynos True Random Number Generator. Note that the kernel needs entropy from the beginning, but gets the possibility to use HWRNG on 14th second of uptime. Reco
